[Choco-users] PalmProblem + ifThen

[Zangitu M. <MZa...@ik...>]

Hello,
I"m now using choco to do some simple check. Here is my program:=20

import choco.Problem;
import choco.integer.IntVar;
import choco.Constraint;

public class test {

  public static void main(String[] args) {

	Problem myPb =3D new Problem();

	IntVar a =3D myPb.makeEnumIntVar("A", 0, 1);
	IntVar b =3D myPb.makeEnumIntVar("B", 0, 1);

	Constraint c1 =3D myPb.eq(a, 0);
	Constraint c2 =3D myPb.eq(b, 1);
	Constraint c3 =3D myPb.ifThen( c1, c2 ); // if a =3D=3D 0 Then b =3D 1
	myPb.post( c3 );

	myPb.solve();

	System.out.println("---------------------------------");
	System.out.println(a + " =3D " + a.getValue());
	System.out.println(b + " =3D " + b.getValue());
	System.out.println("---------------------------------");
  }
}

and it runs

but when I change the Problem to PalmProblem (because I want use later
the Explanation concept) :

import choco.Problem;
import choco.integer.IntVar;
import choco.Constraint;
import choco.palm.PalmProblem;
import choco.palm.integer.PalmIntVar;
import choco.palm.integer.PalmIntDomain;
import choco.palm.explain.Explanation;
import java.util.Set;
import java.util.Iterator;

public class test {

  public static void main(String[] args) {

//	Problem myPb =3D new Problem();
	Problem myPb =3D new PalmProblem();

	IntVar a =3D myPb.makeEnumIntVar("A", 0, 1);
	IntVar b =3D myPb.makeEnumIntVar("B", 0, 1);

	Constraint c1 =3D myPb.eq(a, 0);
	Constraint c2 =3D myPb.eq(b, 1);
	Constraint c3 =3D myPb.ifThen( c1, c2 ); // if a =3D=3D 0 Then b =3D 1
	myPb.post( c3 );

	myPb.solve();

	System.out.println("---------------------------------");
	System.out.println(a + " =3D " + a.getValue());
	System.out.println(b + " =3D " + b.getValue());
	System.out.println("---------------------------------");

	Explanation expl =3D ((PalmProblem)myPb).makeExplanation();
	((PalmIntVar)b).self_explain(PalmIntDomain.VAL, 0, expl);
	System.out.println("Why " + b + " !=3D 0");

	Set set =3D expl.toSet();
	Iterator i =3D set.iterator();
	while (i.hasNext())=20
		System.out.println(i.next());
   =20
	System.out.println("---------------------------------");
  }
}

it goes wrong  :

** JPaLM : Constraint Programming  with Explanations
** JPaLM v0.9b : (July, 2004), ............................
Exception in thread "main" java.lang.NullPointerException
	at choco.palm.PalmProblem.post(Unknown Source)
	at test.main(test.java:24)

So, I call you all for help
Thank you,
Martin